Optical sensor

ABSTRACT

In a sensor, in which light beams are emitted in various directions, reflected at objects that may be present, received again and evaluated according to direction and transit time in the sense of a three-dimensional imaging of the objects, light sources are arranged in the form of a two-dimensional matrix for generating the light beams.

FIELD OF THE INVENTION

The present invention relates to a sensor, in which light beams areemitted in various directions, reflected at objects that may be present,received again and evaluated according to direction and transit time inthe sense of a three-dimensional imaging of the objects.

BACKGROUND INFORMATION

Sensors known as lidar sensors (i.e., light detection and ranging) areavailable on the market. Distinction is made between two different typesof construction, namely, sensors having a fixed measuring-beamarrangement in a horizontal plane, for example, and those havingmechanical beam swinging, e.g., through mirrors. Although the mechanicsallow a finer angular resolution than is possible in the case of afixed, rectilinear measuring-beam arrangement, they have the knowndisadvantages of a mechanical design approach, namely, sensitivity tomechanical stress, wear and tear, and relatively costly production.

The known lidar sensors may be used for assistance systems for motorvehicles on the basis of surround field sensors, for object detection,and for measuring distances and relative velocities. The ACC function(i.e., adaptive cruise control, also known under brand trademarks suchas Abstandsregeltempomat (proximity-controlled cruise control) andDistronic) is presently in the fore, a measuring range of approximately3 m to 120 m with a narrow aperture (beam) angle being necessary. In theautomotive sector, a number of functions can be realized in the closerange up to 30 m distance such as “low speed following”, “blind spotdetection”, “backing aid” or “precrash” using lidar sensors, if a widesensing range exists both horizontally and vertically, with sufficientlyhigh angular resolution in both directions.

An object of the present invention is to provide a sensor for thispurpose, which, in particular, satisfies the demands in the automotiveindustry with respect to manufacturability, reliability, robustness andservice life.

SUMMARY OF THE INVENTION

This objective is achieved in the sensor of the present invention byarranging light sources in the form of a two-dimensional matrix forgenerating the light beams.

Because of the lack of mechanically moving parts, the sensor of thepresent invention has a longer service life, even under roughenvironmental conditions, e.g., vibration. In addition, due to theplanar layout of the light sources and, optionally, optical devices on aprinted circuit board, manufacturing expenditure is low.

In certain applications, it may be advantageous if the light sources areat different distances from one another.

With regard to easy producibility of the sensor according to the presentinvention with the aid of available component parts, according to onefurther development, it can be provided to arrange the light sources onrectilinear subassemblies. However, manufacturing methods are certainlyknown which permit the mounting of the light sources as individualcomponents on a printed circuit board, e.g., using chip-on-boardtechnology.

In another embodiment of the invention, the individual light sources arestaggered in zigzag fashion, in each case within one column.

In addition to the advantages cited, one refinement of the sensoraccording to the present invention has the advantage of greatflexibility, because the light sources are controllable independently ofone another.

Thus, for example, the sensing range may be adapted very quickly duringoperation to the driving situation or the object scene, so that, forinstance, quickly moving objects may be selectively tracked. Thiscapability is especially important for safety-related functions such asprecrash.

Suitable processors to be programmed and other electronic circuits areavailable for the electronic control of the individual light sources.Thus, for example, the type of control of the light sources can bechanged very rapidly in continuous operation; for instance, it ispossible to switch over into several measuring modes having differentangular sensing ranges and measuring cycle times, depending on therequirement. A complete sweep of the entire range may be accomplishedthrough line-by-line scanning of the measuring beams, given relativelylong cycle times. Alternatively, a line scanning or column scanning at aspecific height and width is possible. Finally, individual measuringbeams may be generated for precise and rapid tracking of individualobjects. In this manner, the simultaneous control of various functionssuch as low-speed following and precrash may be accomplished bycoordinated switchover between the various measuring modes of a singlesensor.

For the mode switchover or attention control, the sensor of the presentinvention may be controlled, inter alia, as follows:

-   -   Cyclically repeated, horizontal line scan on the middle plane        −30° to +30° from the horizontal.    -   The higher and lower planes are also scanned at greater time        intervals, in order to determine the vertical object positions,        as well as the position of the vehicle relative to the road        surface.    -   Switchover to a lower or higher plane for the next line-scan        cycles according to need (influence of pitch angle or road        curvature).

In the sensor of the present invention, the light sources may be formedby light-emitting diodes or laser diodes.

According to one advantageous embodiment, a collective lens may bedisposed in front of each light source. In principle, it is possible todesign this collective lens for forming the light beams. Often, however,one will prefer to use the collective lens to concentrate as much lightemitted by the respective light source as possible onto a commoncollective lens, which may also be implemented as a combination ofseveral lenses.

Going into details, the cross-sectional form of the light beam may beimportant, depending on the application. To that end, in one furtherrefinement of the invention, optical waveguides may be provided forshaping the light beams of the individual light sources.

For example, if different angular resolutions are needed in twodirections perpendicular to each other, it may be advantageous if thelight beams emitted by the individual light sources have ellipticalcross-sections.

The present invention also includes that an optical receiver having acollective lens and a light-sensitive area is provided for receiving thebeams reflected by the objects. In this context, the light-sensitivearea may be formed by an optoelectric receiver, e.g., by a suitablylarge-area PIN diode.

Another possibility for advantageously implementing a receiver is forthe light-sensitive area to be formed by optoelectric receivers arrangedin a matrix configuration. The advantage of this arrangement lies, firstof all, in the higher switching speed of the small diodes, resulting ingreater measuring accuracy and a radial separation capability, andsecondly, in the greater angle selectivity, which becomes noticeable inthe avoidance of cross feed between the measuring beams. Intermediatedesign approaches, such as an array of column-shaped PIN diodes, mayalso be used for the two specific embodiments of the light-sensitivearea.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic representation of the arrangement of lightsources in a matrix.

FIG. 2 shows a schematic representation of a motor vehicle provided withtwo sensors according to the present invention.

FIG. 3 shows a schematic representation of a cross-section through asensor having a transmitter and a receiver, respectively.

FIG. 4 shows another specific embodiment of a receiver.

DETAILED DESCRIPTION

FIG. 1 shows ten rows (lines) of light sources 1, each having anelliptical cross-section. The vertical angular coverage achievable witha predetermined lens extends between −10° and +12° in this example. Asthe vertical angular coverage becomes greater, the distance of the rowsfrom one another becomes greater, starting from 0°. This takes intoaccount the circumstance that, in general, a more precise angularresolution is necessary in the horizontal plane at the level of thesensor installation position.

Moreover, in the example, the distances between the light sources arechosen to be greater in a left part of the matrix, so that the angularresolution is less here. At the same time, the light sources with lowvertical angular coverage are staggered in this area, so that, forexample, vertical edges of objects can be detected with relatively goodresolution, in spite of the greater distance.

FIG. 2 shows a motor vehicle 1 on a road 2, with an indicated coverage(sensing) space formed by two sensors (not shown in detail), which emitlight beams 3 and receive reflections from objects. As shown in FIG. 1,in the case of the sensor located on the right side of the vehicle, theangular resolution was reduced to 4° at the left side, compared to 2°throughout the remaining horizontal sensing range and vice versa. Thismeasure saves on light-emitting diodes, but also becomes advantageouslynoticeable in that, all in all, a smaller cycle time is possible, whileretaining the resolution in the more important region.

FIG. 3 shows a sensor of the present invention having a transmitter 11and a receiver 12, each having a lens 13, 14. On a printed circuit board15 of the transmitter are light-emitting diodes 16, arranged, forexample, with the distribution shown in FIG. 1, each provided with alens 17 that causes the greatest possible portion of the light generatedby the light-emitting diode to fall on lens 13, and therefore be usedfor the light beam. Light-emitting diodes 16 are disposed in the focalplane of lens 13, so that the light generated in each instance by alight-emitting diode 16 produces a bundle of parallel rays 18. Bundle ofrays 19, reflected by an object (not shown), is concentrated in receiver12 of the exemplary embodiment according to FIG. 3, onto a point oflarge-area PIN diode 20.

A suitable electronic control circuit 21 is used for the pulsed,sequential driving of light-emitting diodes 16, various modes beingpossible depending on the application case. The information as to whichlight-emitting diodes 16 emit light at what time is transferred to anevaluation circuit 22 of the receiver, so that the pulses generated byPIN diode 20 may be assigned to the light pulses emitted bylight-emitting diodes 16, the transit time then being ascertained.Consequently, in turn, together with the direction information of thelight beams, a three-dimensional image of the detected scene may becreated.

FIG. 4 shows an alternative 23 for receiver 12 (FIG. 3) having a printedcircuit board 24, on which a number of PIN diodes 25 corresponding tothe transmitter are arranged, which, as described at the outset,permits, inter alia, an increase in security against cross feed betweenthe individual light beams. Evaluation circuit 26 of receiver 23 has acorresponding number of inputs.

1-15. (canceled)
 16. A sensor comprising: light sources situated in theform of a two-dimensional matrix for generating light beams emitted invarious directions; means for receiving light beams reflected byobjects; and means for evaluating the received light beams according todirection and transmit time in the sense of a three-dimensional imagingof the objects.
 17. The sensor according to claim 16, wherein the lightsources are at different distances from each other.
 18. The sensoraccording to claim 16, wherein the light sources are situated oncolumn-shaped subassemblies.
 19. The sensor according to claim 16,wherein the light sources are mounted as individual components on aprinted circuit board.
 20. The sensor according to claim 16, wherein theindividual light sources are staggered in zigzag fashion, in each casewithin one column.
 21. The sensor according to claim 16, wherein thelight sources are controllable independently of one another.
 22. Thesensor according to claim 16, wherein the light sources includelight-emitting diodes.
 23. The sensor according to claim 16, wherein thelight sources include laser diodes.
 24. The sensor according to claim16, further comprising a collective lens situated in front of each lightsource.
 25. The sensor according to claim 16, further comprising acommon collective lens.
 26. The sensor according to claim 16, furthercomprising optical waveguides for shaping the light beams of theindividual light sources.
 27. The sensor according to claim 16, whereinthe light beams emitted by the individual light sources have ellipticalcross-sections.
 28. The sensor according to claim 16, wherein the meansfor receiving includes an optical receiver having a collective lens anda light-sensitive area for receiving the beams reflected by the objects.29. The sensor according to claim 28, wherein the light-sensitive areaincludes an optoelectric receiver.
 30. The sensor according to claim 28,wherein the light-sensitive area includes optoelectric receiverssituated in a matrix configuration.